Introduction: How to Solder SMD Parts
In this instructable I’m gonna show you 3 methods to solder SMD parts but before we get to the actual methods I think it’s best to talk about the type of solder to be used. And there are two main types of solder that you can use, that is leaded or lead free solder. If you are doing prototype work it’s best to stick with leaded solder or solder paste because it’s easier to get right, it has a lower melting temperature. If you are doing production work, you plan to sell those boards, than you might be forced to use lead free solder to be compliant with the regulation.
So I’ll be using leaded solder in this video because I am only doing prototype work. Now let’s talk about the methods I use for soldering smd parts. I use 3 different methods, each has advantages and disadvantages.
Step 1: Watch the Tutorial Video!
The video describes the entire process of soldering SMD components, all three methods so I recommend watching the video first to get an overview of the process. Then you can come back and read the following steps for more detailed explanation.
Step 2: Order the Supplies Needed
To do SMD soldering you are going to need some supplies like: solder wire, solder paste, flux, soldering iron so here are a few links to help you find those items. Go ahead and order these to have them ready when you start soldering. You might already have some of these supplies if you have been doing some previous soldering.
Step 3: Method #1: Soldering Directly to the Pcb With a Soldering Iron
This is the method I use when I assemble one or two pieces and I don’t really care about how it’s going to look. I just hold a component with my tweezers and then using some fine solder I solder each component manually. Using some extra flux will certainly help here and is recommended. This method is fast when you have a small to medium size board but becomes very difficult to do this reliably if you go below 0603 smd package. The pads will be too small and you will start to need magnification.
Step 4: Method #2: Using a Stencil to Apply Solder Paste and Heating With Hot Air
This method will require ordering a stencil together with your pcbs but most prototyping friendly fab houses are now offering affordable stencils. You will need to align the stencil over your PCB on a flat surface, then using a squeegee and some solder paste you will scrape across the surface of the stencil. Solder paste will flow through the stencil and end up precisely on each pad on your PCB. Next you will need to place the parts with light pressure, just enough to make them stick to the solder paste. And now the final part is to heat the solder paste up to melting temperature. I tend to use the hot air gun for this because it’s quick but you have to be very careful to have the air pressure low because you can easily blow away components.
You need to be careful if you have other components nearby that can melt, like plastic connectors and also avoid heating electrolytic capacitors too much. SMD parts are usually designed to withstand reflow temperatures for a defined period of time. But you need to stay below 230 degrees C to avoid causing any damage in the case of lead free paste.
Another variation of this method is to use a hot skillet or an iron and heat the pcb entirely from the bottom up. This will provide better results than the hot air gun because the heating will be happening uniformly across the entire surface of the board and there is not risk of blowing the parts away. Using this method I can easily solder 0402 components with great solder joints.
Step 5: Method #3: Using a Stencil to Apply Solder and Reflowing With an Oven
This method uses a stencil for dispensing the paste on to the PCB but for the actual heating of the board a reflow oven is used because it provides an enclosed space where temperature can be controlled precisely. You can build your own reflow oven by re-purposing an electric oven and making your own reflow oven controller. There are plenty of open source designs that you can use and they all use the same principle a PID loop A thermocouple for measuring temperature and a solid state relay for switching the oven on or off according to the program. Using such a setup you can follow a reflow profile which is usually given in the datasheet of the solder paste or the datasheet of the component. This is the same process used in industrial pcb assembly, the only difference is that they have more complicated ovens with different zones and some are filled with specific gasses instead of air to provide the best possible solder joint.
I have built my own reflow oven 7-8 years ago and I’ve used it successfully for assembly thousand of boards. However in recent years I haven’t used it because I only assemble 1-2 prototypes and I tend to use method #1 or #2 because it’s faster and more economical.
You can also buy ready made reflow ovens from China, those are decent from the reviews I’ve seen and there is even an alternative firmware for them that you can load. So if you are not on a tight budget you can also buy one of those. Not really needed for prototyping work but certainly needed if you are assembling more boards, especially if you plan to sell your boards.
Step 6: Conclusion
So there you go, these are the 3 methods I use to assemble SMD parts. If the board also contains through hole parts, I will solder those after I finished assembling the SMD parts. I hope you found this instructable interesting, let me know what you think in the comments section and don’t forget to hit the like button. See you soon.
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What temperature should the soldering iron be set to? I have a variable soldering iron up to 60w; is 40w too low?